Interjection

1. An exclamatory interjection roughly equivalent to 'by God', 'goodness gracious', 'for goodness' sake'.

   1905 That's the trouble -- it was too easy for you -- you got reckless -- thought you could turn me inside out, and chuck me in the gutter like an empty purse. But, by gad, that ain't playing fair: that's dodging the rules of the game. — Edith Wharton, House of Mirth.

Verb

1. To move from one location to another in an apparently random manner; often as phrasal verb gad about.

   1852' "This, I suppose, is the virgin who abideth still in the house with you. She is not given, I hope, to gadding overmuch, nor to vain and foolish decorations of her person with ear-rings and finger-rings, and crisping-pins: for such are unprofitable, yea, abominable. — Alice Cary, Clovernook ....

Noun

1. A sharp-pointed object; a goad.

   December 17, 1885 Twain finds his voice after a short search for it and when he impels it forward it is a good, strong, steady voice in harness until the driver becomes absent-minded, when it stops to rest, and then the gad must be used to drive it on again. — Detroit Free Press.

2. A pointed metal tool for breaking or chiselling rock, especially in mining.
   • 2006, Thomas Pynchon, Against the Day, Vintage 2007, p. 327:

     Frank was able to keep his eyes open long enough to check his bed with a miner's gad and douse the electric lamp

3. A wedge-shaped billet of iron or steel.
4. An old English indeterminate measure of metal produced by a furnace, perhaps equivalent to the bloom, perhaps weighing around 100 pounds.

   1957 Twice a day a 'gad' of iron, i.e., a bloom weighing 1 cwt. was produced, which took from six to seven hours. — H.R. Schubert, History of the British Iron and Steel Industry, p. 146.